Catheters are elongate flexible instruments navigated through natural body lumens of a patient to serve as a conduit for performing a medical procedure at a remote location in the human body. Because the catheters are small and can be navigated through passageways that already exist naturally in the body, the invasiveness of the procedure is minimized. Minimizing trauma associated with the procedure reduces risk to the patient and costs for the medical care provider. In catheter design, there are two prominent design objectives that require conflicting design configurations in order to be achieved. First, is the necessity to make the catheter as small profile as possible to minimize trauma to the patient and to facilitate navigation through narrow passages in the anatomy. The second design consideration is to make the interior passages of the catheter large enough to easily accept other instruments or to provide passage for fluid delivery or aspiration. Of course, reducing the profile of the catheter impinges on the amount of space available to accept instruments and fluid passageways through the catheter that are needed to carry out the medical procedure. The challenge of making a catheter of small profile is especially difficult in designs that employ multiple lumens through the catheter to accept one or more instruments or fluid passageways simultaneously.
In all catheter designs, perhaps the most crucial area for maintaining a reduced profile is at the distal tip of the catheter. The distal tip is the leading area of the catheter as it is navigated into a body lumen and to a treatment site. A small profile at the distal tip of the catheter facilitates penetration through small openings and expands them gradually as the wider more proximal areas of the catheter shaft proceed through.
Biliary procedures in which the Papilla of Vater must be cannulated in order to access the common bile duct can be especially challenging. The papilla is a natural orifice at the end of the common bile duct that is surrounded by the sphincter muscle, which can keep the opening tightly closed. In a biliary procedure, an endoscope is navigated to a location adjacent the papilla and a biliary catheter is inserted through the endoscope and extended through the distal port of the scope. The catheter is advanced to enter the papilla and common bile duct to carry out a biliary procedure such as stone removal or stenting. Failed attempts to cannulate the papilla can serve to irritate it, making it even more difficult to penetrate. Special biliary catheters called papillatomes have been developed that employ an RF energized cutting wire to make a small cut in the papilla during cannulation to increase the diameter of the passage and facilitate penetration. The small cut in the papilla also may serve as effective treatment to allow stones trapped in a bile duct to pass freely through the papilla. Despite the presence of a cutting wire on the papillatome catheter, an effective low profile tip is still desirable to help facilitate entry and positioning of the papillatome in the papilla. The smaller the diameter of the tip of a papillatome, the easier it will be to insert into the small or closed opening of the papilla.
In a biliary catheter such as a papillatome it is also desirable to have a relatively short tip length between the distal end of the tip and the beginning of the exposed cutting wire. The distance between the entry to the common bile duct at the papilla and the first junction in the common bile duct (the segment known as the intramural segment) is 2-8 mm. The Y-shaped junction splits the common bile duct into the pancreatic duct and the bile duct. After cannulation of the papilla the option to proceed into the either duct must remain available to the physician. However, if the tip length of the catheter is relatively long, such as 8 mm or greater, the distal tip may already be positioned beyond the junction after cannulation with the cutting wire at the papilla. With the tip in one duct or the other, selection of the other duct is difficult. A short tip catheter with a tip length distal of about 5 mm or less would be more likely not to extend beyond the junction of the common bile duct after cannulation, thus facilitating navigation into the desired duct for treatment. Also a shorter tip length provides the user with more control over the orientation of the papillatome tip during use. A short tip length also reduces the length of catheter that must be inserted before the exposed cutting wire reaches the papilla and cutting can begin.
As stated above, among the design considerations for a catheter, and in particular a papillatome catheter is providing sufficient space through the interior of the catheter so that other instruments and fluid channels can be provided through the device. Providing multiple lumens in the catheter shaft is one way to enhance the utility of the catheter as a conduit for other devices and treatments. In particular, two or three lumen papillatomes are desirable so that individual lumens can be provided for the cutting wire, a guidewire and a separate lumen for contrast media injection. Not only is it desirable to provide multiple lumens in a papillatome catheter, but also there is a need to make the lumens as large as possible. It is desirable to provide a separate contrast injection lumen, in which a larger diameter helps to insure that the sticky, viscous contrast media can be injected freely at pressures that are easy to modulate. A large guidewire lumen is desirable such that a relatively stiff guidewire providing good pushability performance, such as a 0.035 inch stainless steel guidewire, can be used to track the papillatome catheter and any subsequent catheters that may be navigated into the common bile duct during the procedure.
In current catheter design, attempts to address all the above design considerations in one catheter leads to compromises of each design objective. Provision of multiple large lumens compromises the ability to provide a low profile distal tip. Though tapering the tip to a reduced profile is one way to address that compromise, tapering the tip to a very low profile over a short distance to provide a short tip length is difficult because wall thickness necessarily becomes reduced to the point where lumens and components within them can be exposed to other lumens or to the exterior of the shaft.
When a catheter of sufficiently low profile to access a tight opening such as the papilla is not available in a size to sufficiently large to accommodate the desired instruments such as a 0.035 inch guidewire, a specialized low profile catheter may be used to start the procedure. However such specialized small catheters are not large enough to receive the larger diameter 0.035 inch guidewire, suitably stiff for carrying out all the steps of a biliary procedure such as permitting exchange of different catheters over it. Instead a specialized low profile catheter sacrifices lumen size to provide the low profile. The reduced lumen size may hinder or prevent certain procedures required to be conducted through the catheter. In a biliary procedure, the largest diameter guidewire usable with such a catheter may be only 0.025 inch. That small diameter guidewire is not sufficiently stiff to provide acceptable pushability or to perform catheter exchanges. Therefore if the low profile catheter is first used to cannulate the papilla, the catheter must then be exchanged, for a larger catheter and then the guidewire exchanged for a larger (0.035 inch) guidewire before the procedure can continue. This additional exchanging activity increases procedure time and risk to the patient.
It would be desirable to provide a catheter that combined the attributes of a low profile tapered distal tip, of a short length and having sufficiently large lumen sizes to accommodate the instruments required for all aspects of the procedure. In particular, it would be desirable to provide a papillatome catheter configured to accommodate a 0.035 inch guidewire yet having a low profile distal tip and a short tip length so that exchanges to use a catheter and guidewire useful solely for cannulating the papilla would not be required. It is an object of the present invention to provide a catheter having a distal tip with a low profile, short length and suitably large lumen sizes and arrangements and methods for manufacturing it.